In a soda boiler, combustion liquor, normally black liquor, is supplied to the furnace through spreaders into the boiler (the reactor). Air is added at the same time, at several levels. Drying, evaporation, vaporisation, combustion, pyrolysis and several other processes that the liquor undergoes take place not only in the liquor and in the volume of gas formed, but also in and above the roasting bed. Since it is ideally the case that these processes take place in local trajectories, comprising different processes in different local volumes, rather than a mixture of processes in a global volume, with as similar processes as possible in all local volumes, careful control of each input control variable is of the utmost importance. Of the three main variables relating to operation that can be influenced—the supply of combustion air, the distribution of liquor (i.e. the location in the reactor at which liquor is supplied), and the spread of the liquor (i.e. the manner in which the liquor is supplied and distributed inside the reactor), the present invention relates to the spread of the liquor.
The atmosphere within the furnace is heavily corrosive for all equipment in the furnace environment, in particular given that the atmosphere also is rapidly changing. Thus, alternation between an oxidising atmosphere and a reducing atmosphere takes place in a soda boiler, combined with a high-temperature environment with attack by an alkali smelt. The lifetime for such items as liquor spreaders, therefore, is normally counted in weeks, rather than months. A well-defined and unchanging localisation of critical components of the spreader is necessary in order to obtain a controlled and longer lifetime. Arrangements and measures in order to protect these critical components are effective only for very small, well-defined volumes, mainly as a result of the chaotic nature of the flow patterns in the furnace and the severe aggression of the thermochemical attack. The difficulties of protecting the said critical components of the spreader are not made any less by the fact that the shortest distance between the inner surface of the furnace and the mechanical equipment outside of the boiler cannot be made shorter than approximately 0.5 m due to the wall of a modern soda boiler (reactor) consisting of high-pressure tubes on the inside, protective walls, insulation and external cladding, which all together give the significant thickness of wall.
These conditions—the aggressive atmosphere and the geometrical limitations—apply also for other equipment in a soda boiler, such as mechanical cleaning equipment, soot blowers, and other flow-based cleaning equipment, together with furnace cameras and other sensors. The present invention can be used also for such equipment.
Similar conditions are present also in other combustion equipment, even if the severe chemical attack is lacking in such combustion equipment. The invention can therefore be used in such other combustion equipment such as, for example, equipment for the combustion of biofuels, bubble bed furnaces, circulating fluidising bed furnaces, and in certain other reactors, such as that used to roast iron pyrites.
The spreader according to prior art technology, which is described in, for example, SE 527676, can be rotated in the vertical direction around horizontal axes, centres of rotation, or pivots outside of the reactor wall. When rotating the spreader unit around such axes, centres of rotation or pivots outside of the reactor wall, the angular position of the spreader nozzle inside the furnace changes at the same time, as does its height and its distance from the wall. Due to the thickness of the wall, this means also that the region, or the volume, within which the spreader nozzle moves is large, and this in turn means that deviations from the ideal positioning of the spreader nozzle and the ideal pattern of spread will be significant, while at the same time the possibility of efficiently protecting the spreader is significantly made more difficult, or made impossible.
It may be desirable during operation of the boiler also to introduce other equipment into the boiler through openings in the boiler wall.
It may be desired to introduce, for example:                rodding arrangements, which are used to mechanically remove by poking deposits in association with openings or located on surfaces inside the boiler in association with the opening, or        soot blowers, which are introduced into the interior of the boiler in order to force with the aid of pressurised air, steam or explosive charges deposits to be released either from walls of the boiler or from tubes inside the boiler, or from both, and        camera equipment, which is introduced for inspection, and        various protective arrangements such as screens or cooling equipment.        
The introduction of such equipment requires a hole to be made in the boiler wall, where the construction of the boiler wall must be altered around the hole, and in those cases in which tubes are integrated into the wall it is necessary to reroute these, giving high costs. It is therefore desirable that the opening in the wall be made as small as possible, such that as few tubes as possible in the boiler wall need to be rerouted.
The aim of the invention is to deal with the set of problems described above. This aim can be achieved through the equipment that is to be introduced into the boiler through an opening in the boiler wall, preferably a nozzle for the distribution of liquor, being such that it can be directed into different angular positions through rotation around a virtual centre of rotation located within the outer surface of the boiler wall.
Since the equipment that is to be introduced or positioned is a nozzle for the distribution of black liquor, this virtual centre of rotation is arranged to coincide with the position from which the fuel is spread adjacent to the opening of the nozzle into the furnace, or in an opening into the boiler. It is preferable that the said virtual centre of rotation is constituted by an imaginary horizontal line, which remains stationary during rotation of the nozzle. It is characteristic of the invention that also the said virtual centre of rotation lacks an axis in its physical meaning in the region of the said centre of rotation in the form of a machinery component that is arranged to be stationary or to rotate and that is supported by bearings.
The particular equipment that is to be positioned in the opening of the boiler is, in the embodiments that are described below, a spreader nozzle for black liquor or fuel. This spreader nozzle is arranged at the outlet of a pipe, denoted a “spreader pipe” below, that extends through an opening in a boiler wall.
The invention has its principal application in soda boilers, where facilitation of protective measures for the critical components of the equipment supplements the process technical advantages of being able to orient the equipment, preferably the nozzle, in different angular positions by rotating it around a centre of rotation inside the reactor or at the level of the boiler wall. The process technical advantages of having better control dominate in other combustion equipment and reactors. Among a number of clear advantages that can be achieved with the location of the centre of rotation at a well-defined and essentially unchanged position within the wall of the reactor offered by the present invention, the following can be mentioned:                The distance of the spreader nozzle to the closest boiler wall does not change when the spreader unit is rotated, and this reduces the risk of the splashing of combustion liquid (liquor) onto the wall, during large changes of angle. This provides not only a gain in efficiency, but also an increase in safety. Liquor or other combustion liquid that runs down the wall may under disadvantageous conditions give rise to an explosion in the boiler.        A fixed position of the nozzle that is independent of the angle of rotation makes it also possible to limit the protection of critical components of the spreader from mechanical, thermal and chemical attack to a smaller area, and thus makes this simpler or more efficient, or both.        The spreader nozzle and the pattern of spread from the nozzle remain stationary relative to fixed supply points for combustion air and relative to the fixed position of the bed at the bottom of the furnace.        If it is necessary to adjust the height of the spreader nozzle, this can be carried out as a separate measure that does not affect the angular setting of the spreader nozzle.        It becomes easier to calculate the combustion process in the reactor if the position of spread is fixed. Nearly all currently used calculation procedures assume in practice that this condition is true, and this is thus a false assumption when using currently available technology.        The opening that is required in the boiler wall for the front part of the spreader unit, comprising at least the actual spreader nozzle itself, to reach inside of the reactor can be made smaller, and this leads to, among other results, considerably lower costs for the rerouting of tubes in the wall of the boiler.        A well-defined positioning of the spreader nozzle in the furnace gives also the possibility for the use of remote monitoring of the distribution, of flame-watch type used in burners. Such remote monitoring may be of major significance for preventing, for example, water-smelt explosions due to a failure of the combustion liquid (the liquor) to be distributed and thus meeting the bed in a collected stream, as a result of erroneous function.        It is not necessary to decrease the angular setting of the spreader nozzle from a large angle before it is possible to withdraw the unit from its operating position to its maintenance position, such as may be necessary according to prior art technology, in order to prevent a component of the equipment colliding with the boiler wall.        A smaller amount of cooling agent is required to cool, and thus protect, critical components of the spreader equipment, than that required with prior art technology, and this means that disturbance to the combustion process as a result of the supply of large quantities of cooling agent can be avoided.        Displacement of the equipment between its operating position (within the furnace) and its maintenance position (fully or partially withdrawn) is facilitated in that it is not necessary to check whether the spreader unit is located at a position that is approved for its withdrawal or introduction. Not only manual methods but also remotely controlled equipment can be used while retaining safety. The same functional advantages are achieved, independently of whether the displacement takes place to and from the operation position along a straight line using wheeled transport or along rails, or through any form of curved movement based on linkage arms, shafts or other machinery components.        
Other characteristics and aspects of the invention and its advantages are made clear by the non-independent claims, and by the following description of some embodiments.